Shane Finneran

AN APPROACH FOR EVALUATING THE INTEGRITY OF PLAIN DENTS REPORTED BY IN-LINE INSPECTION TOOLS

Current federal regulations in the U.S. require excavation of plain dents identified through in-line inspection surveys based primarily on depth. Industry experience, and previous research, has shown that the depth of the dent, alone, is not sufficient to assess dent severity and that releases could occur at dents below the excavation threshold (Dawson, 2006). Canada’s National Energy Board released a safety advisory on June 18, 2010, to all companies under their jurisdiction regarding two incidents involving shallow dents. The safety advisory stated that all integrity management programs should be reviewed and updated where appropriate to address the threat posed by shallow dents. Similar incidents have raised awareness in the United States and elsewhere around the world. This paper focuses on the fitness for service of dents identified by in-line inspection surveys. The fitness for service assessment provides an estimated remaining life of a dent based on the geometry of the dent and current pressure cycling of the pipeline. Dynamic pressure cycling at each dent location is estimated using the upstream and downstream pressure cycle data, elevation, and distance along the pipe. The dynamic pressure cycle data at each dent is then converted into equivalent stress cycles based on the results of rainflow cycle counting. Maximum strain levels of the dents are calculated based on the geometry of the dent as determined by radial sensor measurements from the in-line inspection survey. The combination of assessment methods provides estimates of remaining fatigue life and peak strain which can be used for prioritizing the investigation and remediation of plain dents in pipelines. Finite element analysis (FEA) is performed for one dent to calculate the maximum strain levels and identify stress concentration areas. These results are compared with the values applied during the fitness for service assessment to validate the accuracy and conservatism of the calculation methods used. An idealized dent will be analyzed to investigate the strain calculations in ASME B31.8 and localize maximum strain values.

Long Term Structural Integrity Considerations for Abandoned Pipelines

There has been increasing interest across the industry to better understand the possible long term risks associated with out of service pipelines. In Canada, the Canadian Energy Pipeline Association (CEPA), Petroleum Technology Alliance of Canada (PTAC), and the National Energy Board (NEB), have undertaken multiple studies to identify and assess the threats related to pipeline abandonment. [1][2][3]The primary hazards typically identified across industry for pipeline abandonment are associated with long term corrosion degradation, potential for creation of water conduits, possible environmental impacts, and potential for pipeline collapse and associated soil subsidence. Unfortunately, little guidance is presently available to the industry for determining remaining structural capacity of a heavily corroded pipeline to establish likelihood, and possible timeline, of collapse, nor for determining possible subsidence magnitudes associated with large diameter transmission lines.This paper presents a technical case study for an assessment approximating the remaining strength of an abandoned pipeline subject to long term corrosion degradation, considering both general metal loss, and randomized pitting and perforation growth. The work presented used a combination of finite element analyses, and existing industry models for determining load bearing capacity of an abandoned pipeline under varying levels of degradation.Copyright

Evaluating Pipeline Ovality Acceptability Criteria for Straight Pipe Sections

Pipe ovalization, a deviation from the circular nominal cross section, is a common occurrence during the manufacturing of pipe sections. Additionally, ovalization can also occur in pipelines during and after installation and construction. CSA Z662-11 [1] provides an acceptance criteria of 5% for pipeline ovality in bends, however there is a variation in acceptance criteria for pipe ovality occurring in straight pipe sections. An industry review of pipeline design, operation, and maintenance codes was conducted to determine the industry acceptance for ovality limits in straight pipe sections. Based upon this industry review, the ovality limits were evaluated against constructability limits, limitations for passage of in-line-inspection (ILI) tools, as well as evaluating the stress in an ovalized pipe section compared to the maximum allowable stress of the pipe. During this review, it was revealed that allowable stress was the limiting factor for pipeline ovality, compared to constructability and ILI tool passage, thus this paper primarily discusses limitations related to remaining strength for ovalized pipe sections. The API 579 Fitness-for-Service assessment was used to evaluate varying levels of ovality to determine acceptability criteria for ovalization in straight pipe. The criteria was first established using a level 2 Fitness-for-Service assessment, which was then evaluated with a level 3 assessment using finite element analysis. This criterion was evaluated using multiple pipeline diameters and wall thickness in order to determine scalability.Copyright

Conceptual Design of a Spiral Wound Pipeline With Manufactured Residual Stresses

There are several common engineering composites that are designed to take advantage of manufactured residual stresses. Concrete may be designed with pre-stressed steel tendons. Engineering ceramic composites may be designed with mismatch in thermal properties of the components to produce residual stresses and enhance crack deflection properties. Metal matrix composites may also be designed with mismatch in elastic properties of the component to enhance crack deflection properties.The objective of this work is to explore the possibility of designing a spiral wound pipe with enhanced mechanical properties. Consider a sheet of steel wound into a spiral in preparation for welding into pipe. Consider then that it is twisted prior to and during welding of the spiral. When the weld solidifies and the torque is released, the pipe would, in principle, maintain some of the stress of the twist. The spiral could be twisted either “inwards” or “outwards” prior to the weld, and the result would be residual tension or compression.This work is based entirely on theory and analysis. Analyses are performed that predict the residual stresses incurred during the proposed manufacturing technique, and the resulting stresses due in-service conditions. In principle, pipe design and manufacture could be adjusted for either onshore pipelines subject to internal pressure, or offshore pipelines subject to hydrostatic pressures at depth. Both possibilities are considered.Copyright

Fitness-for-Service of Steam-Methane Reformer Hot Outlet Manifolds

A majority of steam-methane reformers (SMRs) have hot outlet manifold systems that operate at temperatures in the range of 750 to 900 °C (1382 to 1652 °F) and internal pressures in the range of 2000 to 3500 kPag (290 to 510 psig). Under these operating conditions, the materials used in the manifold systems, including weld joints, are subject to degradation from high-temperature creep. Thus, fitness-for-service (FFS) assessment of the manifold systems requires evaluation of material degradation as a result of creep damage (voids, micro-fissures and cracks) and creep deformation (strain). This paper reviews a general approach to FFS assessment of SMR hot outlet manifold systems. Using data on operating temperature, pressure, and time in service stresses and strains in the manifold sections are calculated by the finite-element method. The calculated stress-strain data are then used to compute creep damage accumulation as a function of time in service for both base metal and weld joints using available creep-rupture data for the materials. These results are then used to predict remaining creep life and establish recommended inspection protocols.Copyright